Surface micromachined mechanical micropumps and fluid shear mixing, lysing, and separation microsystems

ABSTRACT

A micropump formed from a monolithic body and rotatable disc contained within the body. The rotatable disc may include one or more prostrusions for drawing a fluid through an inlet and expelling it through an outlet. The protrusions may be formed in a spiral formation, extend as radial vanes from a central point, or have another configuration. The micropump may have a thickness no more than about 12 microns. In other embodiments, the rotatable disk includes one or more gears that utilize positive displacement to pump fluids. The micrompump may be used with other microelectromechanical systems and devices.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/422,548 entitled “SURFACE MICROMACHINED MICROPUMPSAND FLUID SHEAR MIXING, LYSING, AND SEPARATION MICROSYSTEMS”, filed onOct. 31, 2002, which is incorporated by reference into the currentapplication in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Development for this invention was supported in part by U.S.Department of Energy Contract No. DE-AO385. Accordingly, the UnitedStates Government may have certain rights in this invention.

FIELD OF THE INVENTION

[0003] The invention is directed generally to micromachined mechanicaldevices, and more particularly, to micromachined pumps capable ofpumping fluids at micro and nano scales and related shear driven mixing,lysing, and separation devices.

BACKGROUND

[0004] Miniature pumps, hereafter referred to as micropumps, are ingreat demand for environmental, biomedical, medical, biotechnical,printing, analytical instrumentation, and miniature coolingapplications. Other typical applications include use of micropumps indrug delivery systems, including both transdermal and impantablesystems, micro total analysis systems, and electronic cooling devices.Just as in lager-scale applications, various pump designs are requiredfor different micropump systems. For certain applications in which spaceis at a premium and in which fluid volumes are small, pumps with minimaldimensions, particularly pump cavity dimensions, are of interest.

[0005] Currently available micropumps typically are fabricated usingetched silicon or glass substrates that are bonded together and utilizean actuation mechanism that most often is a piezo-electric bimorph, orin the case of electrokinetic micropumps, embedded electrodes.Typically, each component is individually bonded to other components toform a pump. As a result, this process is labor intensive and expensive.The resulting high price of the micropumps may preclude profitablecommercialization of these micropumps. Moreover, the bonding of aplurality of components renders these pumps susceptible to reliabilityproblems, such as separation of the bonds.

[0006] Thus, a need exists for an efficient, inexpensive micropump thatis capable of being produced in mass quantities with little or noassembly required.

[0007] In addition, many fluids of interest in microfluidic applicationsare biological or contain complex chemical mixtures. Such solutionsoften must be analyzed or manipulated to separate a constituent ofinterest or to mix in chemical reagents. Because the flow inmicrofluidic devices essentially is laminar having a low Reynoldsnumber, it is difficult to complete these tasks using the turbulence andinertia based methods effective at larger scales.

[0008] Also, in certain applications it can be necessary to lyse cellsin order to access cellular constituents (e.g. DNA or RNA). Typically,cell lysis is accomplished using a centrifuge or sonication in a beadsolution. However, neither method is readily scaleable to microdevices.Therefore, a need exists for microfluidic cell lysis, mixing andseparation devices.

SUMMARY OF THE INVENTION

[0009] This invention is directed to micropumps formed from monolithicstructures having thicknesses of no more than about 12 microns andinclude pumping chambers with inlets and outlets, and structures formechanically urging fluid from the inlet to the outlet. The micropumpsmay be capable of pumping fluids on the micro and nano scales. Each ofthese pumps may be capable of being produced complete with the actuationand transmission mechanisms in batches of hundreds to thousands perbatch using surface micromachining. Consequently, pumps according tothis invention can provide increased reliability and can be producedwith little, if any, costs associated with manual assembly.

[0010] Micropumps embodiments include viscous micropumps and ring gearmicropumps. The viscous micropumps include spiral micropumps,centrifugal micropumps, and micropumps without spiral protrusions, whichare referred to as Von Karman micropumps. The ring gear micropumpsinclude crescent micropumps and planetary gear micropumps.

[0011] According to one aspect of this invention, a micropump, referredto as a spiral micropump, includes a rotatable disk and a stationaryplate. A spiral protrusion is attached to the rotatable disk and draws afluid through an inlet port in the micropump. The fluid passes through aspiral channel formed by the spiral protrusion and between the rotatabledisk and stationary plate. The fluid is expelled through an outlet port.The rotatable disk and stationary plate may be sealed with a variety ofseals, which may include, but are not limited to, a seal resembling alabyrinth or a housing.

[0012] In another embodiment of this invention, a micropump isconfigured identically to the spiral micropump, but does not include thespiral protrusion. This micropump is referred to as the Von-Karman pumpand operates using the viscous drag that develops in the fluid in themicropump as the rotatable disk rotates. This embodiment is advantageousbecause this micropump is not limited by the small aspect ratio thatcharacterizes surface micromachined devices.

[0013] In yet another embodiment of this invention, a micropump isconfigured to include a radial array of vanes attached to a gear diskthat defines an impeller of the micropump. This micropump is referred toas the centrifugal micropump.

[0014] Certain pumping devices described herein can generate a shearfield. Such a field can be used to lyse cells at the microscale wherecentrifugation and sonication are less effective. Also, by positioningdifferent solution constituents at different streamlines in the shearfield, cells can be separated and eluted at the end of the micropumpaccording to their position in the shear field. Those constituentsclosest to the moving plate will be eluted first and those constituentsclosest to the stationary plate will be eluted last. This type ofconstituent separation can be enhanced by operating the shear pumpagainst a pressure gradient. Methods of manipulating constituents as totheir location in different layers of a varying cross-stream shear fieldinclude but-are not limited to electrical fields (AC and DC),hydrodynamic forces, sedimentation forces, thermal gradients anddiffusion.

[0015] Other embodiments of this invention include ring gear micropumps.One type of ring gear micropump is a crescent micropump that is formedfrom a ring gear having a plurality of teeth on its inner and outersurfaces. The teeth on the inner surface are configured to mesh with anidler positioned within the inner aspects of the ring gear, and theteeth on the outer surface are configured to mesh with teeth on atransmission gear used to drive the ring gear. The micropump includes aninlet port and an outlet port in the inner aspects of the ring gear. Thecrescent micropump further includes a crescent shaped component forpositioning the idler and the ring gear relative to each other. Thecrescent micropump operates by rotating the ring gear using, forinstance, a transmission gear, which in turn causes the idler to rotate.The rotating idler draws a fluid from the inlet port and expels thefluid through the outlet port.

[0016] In yet another embodiment of a ring gear micropump, themicropump, referred to as a planetary gear micropump, is composed of aring gear having a sun gear and first and second planetary gearspositioned in interior aspects of the ring gear. The ring gear has aplurality of teeth positioned on an inner surface of the ring gear thatmesh with the planetary gears. The sun gear is coupled to a pivotpositioned eccentrically within the sun gear, and the diameter of thefirst planetary gear may be larger than the diameter of the secondplanetary gear.

[0017] This micropump is operable by rotating the ring gear, whichcauses the planetary and sun gears to rotate. The eccentric pivot causesthe sun gear to rotate around the pivot and oscillate. This oscillationcreates successive increasing and decreasing volumes on either side ofthe sun gear and the first and second gears, which draws fluid into themicropump through an inlet port and expels fluid out of the micropumpthrough an outlet port.

[0018] The various gearing systems and mechanisms of the ring gearmicropumps can be used to move fluids continuously through the micropumpusing positive displacement. The gears may also act to lyse cells, whichis also referred to as cell lysis, when a cellular solution is pumped bythe gears.

[0019] An advantage of micropumps according to the invention is that themicropumps have a monolithic body. For example, these pumps may beconstructed using Sandia National Laboratories' Ultraplanar Multi-levelMEMS Technology (SUMMiT™) process or similar process. As the micropumpsformed by this process are monolithic, the micropumps do not requireadditional assembly. The SUMMiT™ process uses three our four movablepolysilicon layers together with one stationary polysilicon layer. Thepolysilicon layers are separated from adjacent layers by sacrificialoxide layers.

[0020] Another advantage of these pumps is their ability to operate inmicro and nano scales.

[0021] Yet another advantage of this invention is that the micropumpscan operate without valves, thereby making the micropumps more reliableand having less components as compared to micropumps having valverequirements. Furthermore, because the pump is continuous flow ratherthan pulsatile flow, a continuously and smoothly varying flow rate maybe generated without use of microfluidic capacitors to dampen theoscillations.

[0022] These and other features and advantages of the present inventionwill become apparent after review of the following drawings and detaileddescription of the disclosed embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which are incorporated in and form apart of the specification, illustrate preferred embodiments of thepresently disclosed invention(s) and, together with the description,disclose the principles of the invention(s). These several illustrativefigures include the following:

[0024]FIG. 1 is a schematic perspective illustration of a partialcutaway of a spiral micropump;

[0025]FIG. 2 is an exemplary spiral micropump coupled to a typicalelectrostatic comb drive system for supplying rotational motion to themicropump;

[0026]FIG. 3 is a cross-sectional view of the spiral micropump of FIG.2;

[0027]FIG. 4 is a picture of a spiral micropump expelling a droplet offluid under experimental conditions;

[0028]FIG. 5(a) is a cross-sectional view of spiral micropump of FIG. 2;

[0029]FIG. 5(b) is a detail view of a portion of the spiral micropump ofFIG. 5(a);

[0030]FIG. 6(a) is a top view of the spiral micropump of FIG. 2including a housing seal;

[0031]FIG. 6(b) is a cross-sectional view taken at section line A-A inFIG. 6(a);

[0032]FIG. 6(c) is a cross-sectional view taken at section line B-B inFIG. 6(b);

[0033]FIG. 6(d) is a detail view of a portion of the spiral micropumpshown in FIG. 6(a);

[0034]FIG. 7 is a schematic illustration of a crescent micropump;

[0035]FIG. 8 is a picture of two exemplary crescent micropumps, themicropump on the left side having a top cover and the micropump on theright side without a top cover;

[0036]FIG. 9 is a cross section of the crescent micropump of FIG. 7;

[0037]FIG. 10 is a schematic illustration of a planetary gear micropump;

[0038]FIG. 11 is a collection of schematic illustrations of themicropump of FIG. 10 in various orientations during operation;

[0039]FIG. 12(a) is a cross-sectional top view of a Von Karmanmicropump;

[0040]FIG. 12(b) is a cross-sectional front view of the Von Karmanmicropump of FIG. 12(a); and

[0041]FIG. 13 is a cross-sectional top view of a centrifugal micropump.

DETAILED DESCRIPTION OF THE INVENTION

[0042] This invention includes numerous embodiments of monolithicmicropumps that are capable of pumping fluids and are configured for usein microelectromechanical systems (MEMSs). These micropumps aremonolithic structures having thicknesses of no more than about 12microns and include pumping chambers with inlets and outlets, andstructures for mechanically urging fluid from the inlet to the outlet.As used herein, the term monolithic refers to the resulting structureobtained from an integrated circuit formation process, which generallycomprises a plurality of lithography, etching, and deposition steps.Thus, no assembly steps, such as bonding steps, are needed as thevarious layers are inherently self-assembled. Although the micropumpsaccording to the invention are fully monolithic, use of this term doesnot preclude substantially free movement of one layer relative toanother layer, such as in the case of a spinning rotatable disk.

[0043] Micropumps according to the invention have a total thickness ofno more than about 12 microns. Thicknesses of the micropumps describedherein are less than the thicknesses of conventional piezoelectricdriven membrane pumps having, which have thicknesses of between about 80microns and about 100 microns. The relatively high efficiency of pumpshaving thicknesses of 12 microns or less is an unexpected result becauseas the thickness is reduced to no more than 12 microns, the Reynoldsnumber decreases and the effective viscosity increases. Therefore, itwould be expected that the low Reynolds number would render pumpsaccording to the invention ineffective. However, it has been found forthickness of no more than about 12 microns, that viscous effectsactually begin aiding pumping as the mechanism for pumping is based onviscous drag and not on inertial effects.

[0044] Embodiments of these micropumps, which are described in detailbelow, include viscous micropumps formed from rotatable discs and ringgear micropumps. The viscous micropumps include a spiral micropump, aVon Karman micropump, which is a spiral micropump without a spiralprotrusion, and a centrifugal micropump. The ring gear micropumpsinclude a crescent micropump and a planetary gear micropump. Themicropumps may be actuated electrostatically using on-chipmicro-engines. Slightly larger meso-scale versions of these pumps can befabricated using more conventional machining techniques and poweredusing small electric motors.

[0045] These micropumps may be used in a variety of applications. Forinstance, these micropumps may be included as a component of anintegrated circuit system and be placed in communication withmicroprocessors, amplifiers, actuators, voltage controllers for theactuators, sensors and other appropriate devices. These micropumps maybe used as a component in microlabs, which may also be referred to as alab-on-a-chip, in medical devices, such as insulin pumps, chemicalsynthesis, for cooling systems in integrated circuits, and otherapplications.

[0046] Each of these embodiments is preferably formed using surfacemachining processes capable of fabricating hundreds or thousands ofdevices together with no part assembly being required. Surfacemicromachined devices are planar in nature, and are characterized byvery shallow depths, such as, but not limited to, no more than about 12microns. The micropumps may be fabricated using Sandia NationalLaboratories' Ultraplanar Multi-level MEMs Technology (SUMMiT™) processor similar process. The SUMMiT™ process uses three or four movablepolysilicon layers together with one stationary polysilicon layer(“Poly”). The polysilicon layers are separated from adjacent layers bysacrificial oxide layers that are removed during the final etch releaseprocess step. See e.g. I-C Compatible Polysilicon Surface Micromachiningby J. J. Sniegowski and M. P. de Boer, Annu. Rev. Mater. Sci. 2000,30:299-333.

[0047] 1. Monolithic Viscous Micropumps

[0048] A. Spiral Micropump

[0049] One embodiment of this invention, as shown in FIG. 1 and referredto hereinafter as the spiral micropump, includes a rotatable disk 12coupled to a stationary plate 14 using a pin joint 16, which ispositioned generally within the center of stationary plate 14. Rotatabledisk 12 includes a spiral protrusion 21 that directs fluids from aninlet port 18 to an outlet port 20. Stationary plate 14 is a generallyflat shaped component and includes two generally flat surfaces. One ofthese flat surfaces is positioned in close proximity to spiralprotrusion 21. In one embodiment, the combined thickness of rotatabledisk 12, stationary plate 14, and spiral protrusion 21 is no more thanabout 12 microns. In at least one embodiment, the spiral micropump maybe formed from as few as 2 silicon layers. However, the sprial micropumpmay be formed from between 3 and 5 silicon layers as well.

[0050] In another embodiment, the micropump contains the componentsdescribed above; however, spiral protrusion 21 is not included. Rather,this embodiment, which is referred to as a viscous micropump, pumpsfluids using viscous phenomena as the driving mechanism.

[0051] During operation, a fluid enters inlet port 18 and flows throughspiral channel 22 to outlet port 20. Spiral channel 22 is formed byspiral protrusion 21 that is bounded by stationary plate 14 on one sideand rotatable disk 12 on the other side. Fluids, with or withoutsuspended particles, are drawn through spiral channel 22 as a result ofa velocity profile created by rotatable disk 12 rotating around pinjoint 16. The velocity profile consists of fluids having velocities thatvary between about zero at the surface of stationary plate 14 and avelocity approximately equal to the rotational velocity of the rotatabledisk at a location proximate to the inner surface 24 of rotatable disk12. Viscous stresses on upper surfaces of the spiral channel 22 allowfluids to be transported against an imposed pressure difference. Thespiral micropump is capable of expelling a sufficient amount of fluidsto produce droplets of fluid visible to the unassisted human eye, asshown in FIG. 4.

[0052] Rotatable disk 12 may be rotated through numerous methods. In oneembodiment, rotatable disk 12 is rotated using an electrostatic combdrive microengine, as shown in FIG. 2, that provides continuousmechanical power transmitted to rotatable disk 12 through a transmission26, which may be a torque amplification gear mechanism operating at12:1. Transmission 26 includes an output gear 28 that includes aplurality of teeth positioned on a perimeter 30 of output gear 28. Theteeth on output gear 28 mesh with the teeth located on the perimeter 30of rotatable disk 12.

[0053]FIG. 3 is a cross-sectional view of the spiral micropump takenthrough the centerline to illustrate the relationships between thelayers forming the spiral micropump. Rotatable disk 12 is formed from apolysilicon layer, which is identified as Poly 4, and stationary plate14 is formed from another polysilicon layer, which is identified as Poly0. Spiral protrusion 21 is formed from three polysilicon layers, whichare identified as Poly 1, Poly 2, and Poly 3, and is anchored torotatable disk 12. This configuration leaves a small gap between spiralprotrusion 21 and stationary plate 14.

[0054] The spiral micropump may be contained using a variety of seals orcomponents for preventing fluids from leaking out. In one embodiment,seal 32 resembles a labyrinth seal positioned around the periphery ofthe spiral micropump, as shown in FIG. 5. The seal 32 can be formed fromthree polysilicon layers. In one embodiment, the three layers may beconcentric and cylindrical. However, the layers are not limited to thisshape or number. Rather, seal 32 may be formed from any other number oflayers or alternative shapes.

[0055] The three layers are positioned between the rotatable disk andthe fixed plate. The inner and outer layers form protrusion extendingfrom the stationary plate 14 and Poly 0, and the middle layer forms aprotrusion extending from the rotatable disk 12 and Poly 4 andpositioned between the protrusions extending from the stationary plate14. The middle layer rotates with the rotatable disk 12. A smallclearance gap is located between adjacent layers. As shown in FIG. 5,the three cylindrical layers are defined by interconnected layersdesignated as Poly 1, Poly 2, and Poly 3.

[0056] In another embodiment, as shown in FIG. 6, seal 32 may be ahousing that nearly entirely encloses rotatable disk 12, stationaryplate 14, and spiral protrusion 21, except for a small opening throughwhich transmission 26 contacts rotatable disk 12. FIG. 6(b) is across-sectional view of the spiral micropump and shows seal 32 formedfrom a top cover 36 that is formed from a Poly 4 layer, a side wall 38that is formed from Poly 1, Poly 2 and Poly 3 layers, and a bottom cover40 that is formed from a Poly 0 layer. Top cover 36 and side wall 38form a closed chamber that surrounds rotatable disk 12 and stationaryplate 14. In this embodiment, spiral protrusion 21 is defined by thePoly 1 and 2 layer and is attached to rotatable disk 12. The Poly 1layer may also include dimples that create protrusions below the spiralprotrusion 21 to improve the seal between the poly layers forming spiralprotrusion 21. Seal 32 may further include a cantilever seal 42, asshown in FIG. 6(d), for reducing leakage from the bottom of pumpingchamber 44 through an opening. Seal 32 may also include a dimple 48,which may be formed by a dimple cut in the Poly 3 layer, for minimizingleakage from the top of pumping chamber 44 through a window.

[0057] Micropumps according to the invention may also be used to lysecells by pumping a cellular solution at a shear rate sufficient todestroy the cell membrane. In addition, the shear field created in thespiral or viscous micropumps can be used to spatially separateconstituents as the constituents are eluted from the micropump.

[0058] In operation, a liquid containing cells is introduced at theinlet 18 of the spiral or viscous micropump. As the rotatable disk 12 isturned rapidly, the solution is pumped towards outlet 20, and a shearfield is developed between rotatable disk 12 and stationary plate 14that is proportional to the velocity of the rotating disk. If theresulting shear stress induced in the cells in solution is high enough,the cell membrane of the cells will rupture, which results in lysis ofthe cells. After the cells rupture, the fluid stream will continue to bepumped out of spiral channel 22 through outlet 20. Cellularconstituents, such as DNA and cell membrane material, may be separatedwhile flowing through spiral channel 22, as described in detail below.

[0059] The shear field developed by a viscous micropump may be used toseparate constituents in a fluid stream flowing through a channel fed bythe pump. Separation of the constituents is possible due to a variationin velocity of the fluid across the fluid stream. In the simplest case,the fluid near rotatable disk 12 is moving at approximately the velocityof the rotatable disk 12, and the fluid near the stationary plate 14 hasa velocity approximately equal to zero, which is the velocity ofstationary plate 14. The velocity varies linearly between zero and themoving disk velocity as the fluid stream is traversed from thestationary plate to the rotatable disk. Because the flow field throughchannel 22 is essentially laminar, constituents stay in layers, orlanes, as the constituents move through the micropump. The constituentsclosest to rotatable disk 12 are expelled from the micropump ahead ofthe slower moving constituents that are located closer to stationaryplate 14. Because of this phenomena, constituents are separated in spaceand time in an exit channel as a result of the constituents occupyingdifferent layers within the fluid flow. The separation betweenconstituents may be increased by increasing the speed of the micropump.For best operation, different constituents should be positioned atdifferent locations across channel 22 in the flow stream. In some cases,such a constituent configuration occurs naturally because of the shearfield. Different constituents occupy different lamina because of the waythe constituents respond to the shear field.

[0060] Constituents may also be positioned in different fluid laminausing other methods.

[0061] For instance, an electrode or an array of electrodes can beincorporated in stationary plate 14 to apply an electric fieldconsisting of alternating or direct current (AC or DC, respectively), tothe electrode or electrodes while rotatable disk 12 is grounded.Rotatable disk 12 may be grounded through the drive mechanism. Thisconfiguration produces an electric field that is generally perpendicularto the direction of fluid flow. The solution constituents are positioneddifferently within the cross-stream field and are therefore, indifferent fluid lamina. The position of the solution constituents isdictated by the constituents' electrophoretic or dielectrophoreticproperties. The electrophoretic properties determine the DC signalresponse, and the dielectrophoretic properties determine the AC signalresponse. Constituents positioned in lamina nearest rotating disk 12,which is the ground, travel further through the micropump in aparticular time period than other fluids.

[0062] Other methods of establishing cross-stream fields includesedimentation processes in which different specific gravity constituentsare positioned at different locations in a cross-stream gravity field,and chemical affinity processes, whereby a wall of a micropump, whetherstationary or rotating, is coated which causes chemical constituents tobe adsorbed and removed from the fluids at different rates. Differencesin diffusion coefficients correlating with different constituents causessome separation of constituents but also leads to broadening of thebands of eluted constituents as the fluids are expelled from themicropump, thereby reducing resolution.

[0063] These separation effects can be enhanced when the pump isoperated against a pressure gradient, such as where the pressure atoutlet 20 is greater than the pressure at inlet 18. This pressuregradient forces the fluids against the flow induced by rotatable disk12. The fluid near stationary plate 14 is more affected by the pressuregradient than the fluid in streamlines located near rotatable disk 12.If the pressure gradient is sufficient, the fluid near stationary plate14 will be pushed backward against the shear driven flow. This causesthe solution constituents to be separated more widely because while thefluid near the stationary wall is pushed back towards inlet 18 by thepressure gradient, solution constituents near rotatable disk 12 arepulled in the usual flow direction.

[0064] While these processes produce constituent separation, the sameprocesses may also be used for constituent mixing. Enhanced diffusion(dispersion) in the shear field occurs when the constituentconcentration gradient across the stream due to along stream convectionreduces the mixing time required. Another method of mixing constituentsis to stop the flow at outlet 20. In this embodiment, a re-circulationsystem is established in which the fluids first travel through themicropump in the forward direction along rotatable disk 12 and thentravel back along stationary plate 14 due to the pressure driven flow inthe low velocity streamlines positioned closely to stationary plate 14.This re-circulation region is an effective microfluidic mixer.

[0065] B. Von Karman Micropump.

[0066] In another embodiment of this invention, a micropump, which isreferred to as a Von Karman micropump is shown in FIGS. 12a and 12 b.The Von Karman micropump is composed of a rotatable plate 82 thatrotates on top of a parallel fixed plate 84 about pin joint 85. A cavity86 is formed between the disk 82 and the plate 84 and for pumping thefluid. The fixed plate 84 has an inlet port 88 and an outlet port (notshown). The viscous forces caused by the rotating flat disk 82 carry thefluid from the inlet port 88 to the outlet port.

[0067]FIG. 12b illustrates a Von Karman micropump that may be formedusing the SUMMiT-V™ process and may have a thickness no more than about12 microns. In at least one embodiment, the Von Karman micropump may beformed from as few as 2 silicon layers. However, the Von Karmanmicropump may be formed from between 3 and 5 silicon layers as well. Thefixed plate 84 may be formed in Poly 0 and the inlet port 88 and may becreated by a Bosch etch through the wafer. The rotatable plate 82 may beformed in the Poly 3 and may create a cavity 86 whereby the rotatableplate 82 is about six microns from the fixed plate 84. The rotatableplate 82 may be driven using gear teeth on the outer surface of therotatable plate 82. The Poly 4 layer may form a top cover 90 that may beconnected seamlessly to the housing walls 92, which may be anchored tothe ground. The housing walls 92 and the Poly 4 top cover 90 provide acontinuous seal around the entire micropump, except for the areaproximate to the driving gears 94. Surface tension forces prevent thefluid in the micropump from leaking through the very small gap proximateto the drive gears 94.

[0068] C. Centrifugal Micropump

[0069]FIG. 13 shows yet another embodiment of a viscous drag micropumpand is referred to as a centrifugal micropump. The centrifugal micropumpmay have a thickness no more than about 12 microns. In at least oneembodiment, the centrifugal micropump may be formed from as few as 2silicon layers. However, the centrifugal micropump may be formed frombetween 3 and 5 silicon layers as well. The configuration of thecentrifugal micropump resembles the spiral micropump; however, thecentrifugal micropump does not include a spiral protrusion. Rather, thecentrifugal micropump includes a radial array of vanes 96 attached to arotatable disk 98. The rotatable disk 98 functions as an impeller of thecentrifugal micropump.

[0070] 2. Monolithic Ring Gear Micropumps

[0071] A. Crescent Micropump

[0072] The invention also includes planar gear pumps, such as thecrescent micropump and the planetary gear micropump, for pumping fluidsand for lysing cells. The planar gear micropumps may have thicknesses nomore than about 12 microns. In at least one embodiment, the planar gearmicropump may be formed from as few as 2 silicon layers. However, theplanary gear micropump may be formed from between 3 and 5 silicon layersas well. The planar gears may be used to lyse cells, as described indetail above, by pumping a cellular solution through the micropump. Thecrescent micropump, as shown in FIG. 7, includes a ring gear 48 having aplurality of teeth on its outer and inner surfaces. In at least oneembodiment, the ring gear 48 may be formed from three or four layers ofsilicon and a base layer 49 may be formed from one or more layers ofsilicon. The teeth on the outer surface mesh with teeth on a drive gear,and the teeth on the inner surface mesh with an idler 52. In thisconfiguration, a drive gear rotates and causes ring gear 48 to rotate,which in turn causes idler 52 to rotate. This action causes a fluid tobe drawn into interior aspects of ring gear 48 from inlet 54 andexpelled through outlet 56. Idler 52 and ring gear 50 are kept inposition with a crescent diverter 58.

[0073]FIG. 8 depicts two crescent micropumps 51 and 53, micropump 51having a top cover in place and micropump 55 having the top coverremoved. The crescent micropumps can be driven with torsional ratchetactuators 60, or other structure for providing rotational motion tomicropumps. Torsional ratchet actuators are independently attached totransmissions 62 for applying rotational motion to ring gears 48. Thecrescent micropump on the right may have a cover installed using a postfabrication technique such as, but not limited to, anodic bonding.

[0074]FIG. 9 depicts a cross-section of ring gear 48 including a seal 64positioned around pumping chamber 66, which is formed as an integralpart of ring gear 48. Seal 64 resembles a labyrinth seal and is formedfrom a dimple in the Poly 1 layer. In addition, seal 64 includes aplurality of rollers that are created using a pin joint process and actas axial bearings that support the walls of the seal during rotation andthus minimize friction.

[0075] B. Planetary Gear Micropump

[0076] Yet another embodiment of this invention, as shown in FIG. 10 andreferred to hereinafter as a planetary gear micropump, may be used topump fluids or lyse cells. The planetary gear micropump may have athickness no more than about 12 microns. In at least one embodiment, theplanetary gear micropump may be formed from as few as 2 silicon layers.However, the planetary gear micropump may be formed from between 3 and 5silicon layers as well. The micropump includes a ring gear 68mechanically coupled to a sun gear 70 using first and second planetarygears, 72 and 74 respectively. Sun gear 70 pivots eccentrically aroundpivot 76 that is not in the center point of sun gear 70. Ring gear 68drives the rotation of first and second planetary gears 72 and 74 andsun gear 70. The diameter of the first planetary gear 72 is larger thanthe diameter of the second planetary gear 74, or vice versa, and the sumof the diameters of sun gear 70 and first and second planetary gears 72and 74 is approximately equal to the pitch diameter of ring gear 68. Thering gear 68 may be formed from three or more layers of silicon. A baselayer may be formed from one or more layers of silicon.

[0077] Operation of the planetary gear micropump is shown in FIG. 11. Asring gear 68 rotates, first and second planetary gears 72 and 74 rotatearound sun gear 70. Rotation of first and second planetary gears 72 and74 around sun gear 70 causes sun gear 70 to rotate because the gap 78between the right side of sun gear 70 and the inner wall of ring gear 68is smaller than the gap 80 between the left side of sun gear 70 and theinner wall of ring gear 68. As sun gear 70 rotates around pivot 76, gap78 continues to shrink in size and sun gear is forced to make a fullrevolution around pivot 76. This eccentric rotation of sun gear 70produces successive increasing and decreasing volumes on either side ofsun gear 70 and the first and second gears 72 and 74. Such actionprovides pumping action necessary for the pump to operate.

[0078] The foregoing is provided for purposes of illustrating,explaining, and describing embodiments of this invention. Modificationsand adaptations to these embodiments will be apparent to those skilledin the art and may be made without departing from the scope or spirit ofthis invention.

We claim:
 1. A micropump, comprising: a pumping chamber, wherein saidpumping chamber includes an inlet for drawing fluid therein and anoutlet for expelling said fluid out of said chamber, and structure formechanically urging said fluid from said inlet to said outlet, whereinsaid micropump is fully monolithic forming a monolithic body, said pumphaving a total thickness of no more than about 12 microns.
 2. Themicropump of claim 1, wherein said pumping chamber includes at least onerotatable disc in fluid communication with said fluid, said structurefor mechanically urging comprising said rotatable disc.
 3. The micropumpof claim 2, wherein the at least one rotatable disc comprises at leastone protrusion extending from the disc.
 4. The micropump of claim 3,wherein the at least one protrusion forms a spiral shaped fluid pathwayconcentric with the at least one rotatable disc.
 5. The micropump ofclaim 3, wherein the at least one protrusion forms a plurality of radialvanes extending from an axis of rotation of the rotatable disc.
 6. Themicropump of claim 2, wherein at least one rotatable disc furthercomprises a plurality of gear teeth on a side surface of the rotatabledisc.
 7. The micropump of claim 6, further comprising at least onecrescent shaped diverter positioned in the pumping chamber proximate tothe at least one rotatable disc, and wherein an inner surface of themonolithic body includes a plurality of gear teeth for meshing with theat least one rotatable disc.
 8. The micropump of claim 2, furthercomprising at least one cap forming a portion of the monolithic body andhaving an opening enabling a driving gear to contact the at least onerotatable disc contained in the monolithic body.
 9. The micropump ofclaim 2, further comprising a labyrinth seal formed from a firstprotrusion forming a ring extending generally vertically from a baselayer and surrounding the rotatable disc, a second protrusion forming aring extending generally vertically from the base layer and positionedinside the first protrusion, and a third protrusion forming a ringextending generally vertically from the at least one rotatable disc andpositioned between the first and second prostrusions.
 10. The micropumpof claim 2, further comprising at least one electrostatic comb drive forrotating the at least one rotatable disc.
 11. The micropump of claim 10,further comprising at least one gear in contact with the electrostaticcomb drive and in contact with the at least one rotatable disc.
 12. Themicropump of claim 11, wherein the at least one gear comprises a 12:1torque amplification gear train.
 13. The micropump of claim 1, whereinsaid pumping chamber includes at least two rotatable gears therein, saidstructure for mechanically urging comprising said rotating gears.) 14.The micropump of claim 13, wherein the at least two rotatable gearscomprises at least three rotatable gears, wherein a first rotatable gearis rotatably attached to a pin substantially at a center point of thebase layer and includes a plurality of gear teeth, a second rotatablegear including a plurality of teeth on a side surface is positionedbetween the first rotatable disc and a side wall of the monolithic body,and a third rotatable gear including a plurality of teeth on a sidesurface and having a diameter larger then the second rotatable gear ispositioned between the first rotatable gear and a side wall of themonolithic body.
 15. A micropump, comprising: a monolithic body formedfrom between about two layers of silicon and about five layers ofsilicon and having a thickness no more than about 12 microns, whereinthe monolithic body comprises a base layer and side walls forming anpumping chamber containing at least one rotatable disc; wherein saidpumping chamber includes an inlet for drawing fluid therein and anoutlet for expelling said fluid out of said cavity; and at least onerotatable disc positioned in the pumping chamber for drawing a fluidthrough the inlet and expelling the fluid out of the outlet.
 16. Themicropump of claim 15, wherein the at least one rotatable disc comprisesat least one protrusion extending from the disc.
 17. The micropump ofclaim 15, wherein the at least one protrusion forms a spiral shapedfluid pathway concentric with the at least one rotatable disc.
 18. Themicropump of claim 15, wherein the at least one protrusion forms aplurality of radial vanes extending from an axis of rotation of therotatable disc.
 19. The micropump of claim 15, wherein at least onerotatable disc further comprises a plurality of gear teeth on a sidesurface of the rotatable disc.
 20. The micropump of claim 19, furthercomprising at least one crescent shaped diverter positioned in thepumping chamber proximate to the at least one rotatable disc, andwherein an inner surface of the monolithic body includes a plurality ofgear teeth for meshing with the at least one rotatable disc.
 21. Themicropump of claim 15, wherein the at least one rotatable disc comprisesat least three rotatable discs, wherein a first rotatable disc isrotatably attached to a pin substantially at a center point of the baselayer and includes a plurality of gear teeth, a second rotatable discincluding a plurality of teeth on a side surface is positioned betweenthe first rotatable disc and a side wall of the monolithic body, and athird rotatable disc including a plurality of teeth on a side surfaceand having a diameter larger then the second rotatable disc ispositioned between the first rotatable disc and a side wall of themonolithic body.
 22. The micropump of claim 15, further comprising atleast one cap forming a portion of the monolithic body and having anopening enabling a driving gear to contact the at least one rotatabledisc contained in the monolithic body.
 23. The micropump of claim 15,further comprising a labyrinth seal formed from a first protrusionforming a ring extending generally vertically from the base layer andsurrounding the rotatable disc, a second protrusion forming a ringextending generally vertically from the base layer and positioned insidethe first protrusion, and a third protrusion forming a ring extendinggenerally vertically from the at least one rotatable disc and positionedbetween the first and second prostrusions.
 24. The micropump of claim15, further comprising at least one electrostatic comb drive forrotating the at least one rotatable disc.
 25. The micropump of claim 24,further comprising at least one gear in contact with the electrostaticcomb drive and in contact with the at least one rotatable disc.
 26. Themicropump of claim 25, wherein the at least one gear has a 12:1 torqueamplification gear train.
 27. A method of pumping fluids, comprising:rotating at least one rotatable disc positioned in a pumping chamber ofa miropump formed from a monolithic body having a thickness no more thanabout 12 microns and containing the at least one rotatable disc; whereina fluid is drawn through an inlet in the pumping chamber and expelledfrom an outlet in the pumping chamber.
 28. The method of claim 27,wherein rotating at least one rotatable disc comprises rotating at leastone disc comprising at least one protrusion extending from the disc. 29.The method of claim 28, wherein rotating at least one rotatable dischaving at least one protrusion extending from the disc comprisesrotating at least one disc having a spiral shaped protrusion extendingfrom the disc.
 30. The method of claim 28, wherein rotating at least onerotatable disc having at least one protrusion extending from the disccomprises rotating at least one disc having a spiral shaped protrusionextending from the disc.
 31. The method of claim 27, wherein rotating atleast one rotatable disc is accomplished using at least oneelectrostatic comb drive.
 32. The method of claim 27, wherein rotatingat least one rotatable disc drives at least one idler gear positioned inthe pumping chamber of the at least one rotatable disc.
 33. The methodof claim 27, wherein rotating the at least one rotatable disc comprisesrotating at least three gears in the pumping chamber.